1. Field of the Invention
The present invention relates to a loudspeaker in which a treble reproduction threshold frequency used in acoustic reproduction equipment is increased.
2. Description of the Related Art
In the past, as a method for increasing a treble reproduction threshold frequency in loudspeakers, a method described on pages 157-158 of xe2x80x9cLoudspeaker Systemxe2x80x9d, 1st Vol., T. Yamamoto (Radio Gijutsusha) has been known. More specifically, according to this method, it is effective.
1. to render a diaphragm system lighter,
2. to permit use of a diaphragm having high stiffness, and
3. to decrease a cone angle at a connected portion between a diaphragm and a voice coil bobbin.
However, a conventional method has the following problems.
First, if a diaphragm system is rendered light, the strength of a diaphragm is decreased. Therefore, nodal resonances of the diaphragm becomes likely to be generated, and a number of peak dips occur in sound pressurexe2x80x94frequency characteristics. Furthermore, resistance to input cannot be increased.
Furthermore, a material for a diaphragm having high stiffness is expensive. Generally, a material having high stiffness has a small internal loss, which causes a large peak dip in sound pressurexe2x80x94frequency characteristics.
Furthermore, if a cone angle at a connected portion between a diaphragm and a voice coil bobbin is decreased, a mild and large peak dip occurs in sound pressurexe2x80x94frequency characteristics due to a cavity effect of the diaphragm.
The cavity effect occurs when a cavity is formed due to a recess on a front surface of a diaphragm of a loudspeaker and this cavity generates resonance in a particular band, causing a peak dip in sound pressurexe2x80x94frequency characteristics.
A loudspeaker of the present invention includes a frame, a voice coil bobbin, and a diaphragm connected to the frame and the voice coil bobbin, wherein the diaphragm is connected to the voice coil bobbin in such a manner that a cone angle between the diaphragm and the voice coil bobbin becomes small enough to obtain a preferable treble reproduction threshold frequency, the diaphragm has a first connected portion connection to the voice coil bobbin and a second connected portion connected to the frame, and the diaphragm has an arch-shaped cross section so as to have a top portion formed outward from both the first connected portion and the second connected portion.
In one embodiment of the present invention, the diaphragm is connected to the voice coil bobbin in such a manner that the cone angle become substantially 45xc2x0 or less.
In another embodiment of the present invention, the voice coil bobbin has a substantially cylindrical shape, and the first connected portion is connected to an end of the voice coil bobbin.
In another embodiment of the present invention, the first connected portion is connected to an outer diameter portion of the voice coil bobbin.
In another embodiment of the present invention, the loudspeaker further includes a connecting section for connecting the diaphragm to the frame and the voice coil bobbin, and the connecting section contains a rubber adhesive.
In another embodiment of the present invention, the first connected portion includes a tapered portion with a tapered shape, and the tapered portion is connected to an inner diameter portion of the voice coil bobbin.
In another embodiment of the present invention, the diaphragm is connected to the voice coil bobbin in such a manner that the tapered portion directly comes into contact with the inner diameter portion.
In another embodiment of the present invention, the frame seals a space on a rear side of the diaphragm, and the diaphragm has a air flow portion which allows air to flow therethrough.
In another embodiment of the present invention, the air flow portion is disposed in the vicinity of an outer periphery of the diaphragm.
In another embodiment of the present invention, the air flow portion is made of a member having a density lower than a member for forming a portion other than the air flow portion.
In another embodiment of the present invention, the air flow portion has a plurality of small holes for allowing air to flow therethrough.
A loudspeaker of the present invention has a structure in which a diaphragm has an arch-shaped cross-section with a top portion curved outward from inner and outer attachment portions, and a cone angle at a connected portion between the diaphragm and a voice coil bobbin is about 45xc2x0 or less. Because of this structure, the cavity effect can be suppressed, and the strength of the diaphragm is improved. Furthermore, a treble reproduction threshold frequency is easily increased by using an inexpensive material while sound pressurexe2x80x94frequency characteristics are flattened.
According to an aspect of the present invention, while a cone angle at a connected portion between a diaphragm and a voice coil bobbin is decreased, the height of the diaphragm can be rendered smaller due to its arch-shaped cross section. This suppresses the cavity effect. Furthermore, because of the arch-shaped cross section, the strength of the diaphragm is improved, and nodal resonances become unlikely to be generated.
According to another aspect of the present invention, a diaphragm can be directly connected to a voice coil bobbin without any adhesive layer therebetween.
According to still another aspect of the present invention, air can flow through a diaphragm, and stiffness of the air in a space on a rear side of the diaphragm can be decreased. Since base resonance is proportional to a square root of stiffness, bass resonance can be decreased, i.e., bass characteristics can be flattened.
Thus, the invention described herein makes possible the advantage of providing an inexpensive loudspeaker in which flat sound pressurexe2x80x94frequency characteristics are obtained while a treble reproduction threshold frequency is increased.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.